Adding new "addrlocal" field to RPC getpeerinfo.

The existing CNode::addrLocal member is revealed to the user,
as an address string, similar to the existing "addr" field.
Instead of showing garbage or empty string,
it simply will not appear in the output if local address not known yet.

src/net.h

@@ -121,6 +121,7 @@ public:
     bool fSyncNode;
     double dPingTime;
     double dPingWait;
+    std::string addrLocal;
 };